Growth kinetics and microstructure characteristics of the Zr-Cr interlayer in a Cr-coated Zry-4 alloy exposed to high-temperature steam

The growth kinetics and microstructural characteristics of the interlayer in a Cr-coated Zry-4 alloy exposed to steam at 1200 °C for up to 10000 s were systematically studied through advanced characterization. A continuous ZrCr2 Laves phase interlayer develops at the coating-substrate interface following a parabolic law. It transforms into a duplex structure composed of a ZrCr2 layer and a thin Zr-Cr-O layer after a longer time of exposure. The growth of the interlayer is nearly terminated, and its thickness remains constant after oxidation for 3000 s. The prior interlayer transforms into the intertwined ZrO2 and metallic Cr stringers after exposure to 10000 s due to the increased oxygen partial pressure inside the interlayer. The mechanisms controlling the formation and evolution of the interlayer are discussed.